Recently, in the field of information and telecommunications, optical communication traffic infrastructures have been built up rapidly for enabling high-speed transmission of massive data, i.e., fiber-optic networks have been implemented in backbone and metro-access network systems for communications over relatively long distances of the order of kilometers. Henceforth, it will be advantageous to implement signal wiring opticalization even for short-distance communications such as rack-to-rack transmission (over a distance of the order of meters to hundreds of meters) and intra-rack transmission (over a distance of the order of centimeters to tens of centimeters) for the purpose of processing massive data without delay.
As regards signal wiring opticalization inside equipment, in a transmission unit such as a router/switch, for example, a high-frequency signal transmitted from an external network such as an Ethernet system through an optical fiber is input to a line card. On one backplane, plural line cards are provided, and a signal input to each line card such as mentioned above is collected to a switch card via the backplane. Then, after the input signal is subjected to processing by an LSI in the switch card, an output signal is furnished to each line card via the backplane again. Where this kind of operation is performed in conventional equipment, a signal having a transfer rate of 300 Gbits/s or higher is collected to the switch card via the backplane. For transmission thereof through use of conventional electrical wiring, it is required to provide divisions each corresponding to a transfer rate of approximately 1 to 3 Gbits/s per wiring line in consideration of propagation loss, i.e., it is required to use at least 100 wiring lines.
Further, it is necessary to provide a pre-emphasis/equalizer circuit for a high-frequency signal transmission line or to provide a countermeasure against reflection or crosstalk between wiring lines. In a technical trend toward still larger capacities of equipment systems for processing information at a higher transfer rate of the order of Tbits/s, the use of conventional electrical wiring will give rise to problematic requirements for a significant increase in the number of wiring lines and effective countermeasures against crosstalk or the like. As a solution to these requirements, it is desired to opticalize signal transmission lines for signaling through a line card, a backplane, and a switch card in equipment, for signaling between boards, and for signaling between chips on a board. Thus, high-frequency signal propagation can be made at a transfer rate of 10 Gbits/s or higher, thereby advantageously contributing to a decrease in the number of transmission lines and elimination of the necessity for above-mentioned countermeasures for high-frequency signal transmission.
For implementation of high-speed optical interconnection circuits that are applicable to signal transmission in equipment, an optical printed circuit board featuring excellent performance and high component mountability must be fabricated at low cost. In Patent Document 1 indicated below, there is disclosed an exemplary embodiment of a high-speed optical interconnection circuit wherein a multilayered optical waveguide array is used to provide optical coupling with a photonic device array at a high level of wiring density. The configuration of this optical interconnection circuit is shown in FIG. 7. In this example, each of optical wiring layer 101A and 101B includes an optical waveguide array having a plurality of lines in a two-dimensional form, and these optical wiring layers are stacked multilayeredly in the direction of board thickness. On the surface of the board, a surface-emitting (surface-sensitive) photonic device array 100 is mounted so as to provide optical coupling. This arrangement is advantageous in that a high level of wiring density is attainable on a smaller mounting area. Further, regarding a mirror part 106 that reflects an optical beam propagating through the optical waveguide array perpendicularly with respect to the board, the end faces of optical waveguide arrays 101A and 101B are disposed in line. Thus, plural cores can be formed simultaneously by cutting or the like, contributing to simplification in the fabrication process step concerned.
Further, in Patent Document 2 indicated below, there is disclosed an exemplary embodiment of an optical interconnection circuit wherein an optical wiring layer and a beam reflection mirror member are formed in an integral structure. In this example, a board having electrical wiring is included, an optical wiring layer is formed to have a core and a clad disposed on at least one face of the board, and a mirror member is embedded between the board and the optical wiring layer to provide an optical-electrical wiring board. This board is produced by a fabrication method including the following steps; disposing a mirror member on a board, and forming an optical wiring layer so as to cover the mirror member disposed on the board. Since the mirror member is disposed on the optical wiring board and the optical wiring layer is so formed as to cover the mirror member, it is allowed to dispose the mirror member at any position on the board, i.e., a mounting layout can be arranged flexibly. Besides, by preparing a mirror member as a separate part and mounting the prepared mirror member on the board, it is possible to obviate degradation in board fabrication yield relevant to a mirror forming process.
Patent Document 1:
Japanese Patent No. 3748528
Patent Document 2:
Japanese Patent Application Laid-Open Publication No. 2003-50329